1. Field of Invention
The present invention generally relates to the AC to DC conversion and more particularly to a half-wave rectifier circuit not requiring a diode.
2. Description of Prior Art
AC to DC automatic gain control (AGC) utilizing AC to DC conversion is necessary for wireless two-way voice (VOX) and keypad employed in alarm systems for adaptation from the analog domain to the digital domain. AGC circuitry automatically controls the gain of a signal so that weaker signals receive more gain and stronger signals receive less gain or none at all.
There are various methods of achieving AC to DC conversion such as full-wave or half-wave rectifier circuits. AC to DC conversion utilizing a half-wave rectifier provides a circuit that allows only the positive portion or the negative portion of an AC signal to pass, while at the same time blocking out the other portion—thus “clipping” the originally imputed signal.
For Example, FIG. 1 illustrates a conventional half-wave rectifier 100, including an operational amplifier 110, with an AC voltage source (Vin) inputted to the inverting input 112. The operational amplifier 110 is configured with negative-feedback loop 120, including non-inverting input 114, Node A, and diode 130. A resistor 140 coupled to ground 150 is coupled to the voltage output at Node B which is further coupled to the output of the negative-feedback loop 120 at Node A.
In operation, conventional half-wave rectifier 100 operates in two modes: Vin>0 and Vin<0. In the first mode, when Vin is greater than zero, output 116 of the operational amplifier 110 will swing positive thereby turning on diode 130. This first mode results in a virtual short where Vout=Vin. In the second mode, when Vin is less than zero, output 116 will swing negative thereby resulting in the current through resistor 140 to equal zero. This second mode results is an open circuit between output 116 and Node A. The result of conventional half-wave rectifier 100 swinging back and forth from positive to negative is a “clipping” of the negative trough from the input sine wave signal.
The disadvantage of utilizing a diode in a half-wave rectifier is that low-level signals below the conduction level of a diode (<0.6 volts for silicon diodes or 0.2 volts for germanium) cannot pass through the half-wave rectifier circuit. Hence, there is a need for an AC to DC converter utilizing a half-wave rectifier without a diode.